The invention relates to a method of quantifying at least one analyte in a liquid medium, this method including a reaction of the analyte with ligands grafted onto magnetic particles contained in the liquid medium.
A quantifying method of this type is known from the document WO 03/044532, which consists in applying a magnetic field to a liquid medium containing the analyte being quantified and magnetic particles functionalized at the surface with specific ligands of the analyte being quantified. The magnetic field has an intensity sufficient to cause the formation of chains or clusters of magnetic particles, and the application thereof to the liquid medium is maintained for a sufficient period of time for the analyte to be coupled or associated with the ligands of the magnetic particles, after which the field is cancelled, thereby causing the separation of those magnetic particles the ligands of which have not reacted with the analyte being quantified. The presence of the analyte in the liquid medium can be determined by direct observation under a microscope or preferably by measuring a parameter such as the optical density of the liquid medium. The concentration of same can also be determined by measuring the variation of the optical density of the liquid medium, between a moment t0, which corresponds to the start of the magnetic field application, and a moment t1, which follows the cancellation of the magnetic field at the end of the reaction between the analyte and the ligands.
The value of the variation in optical density between t0 and t1 is compared with calibration curves or values obtained with known concentrations of the analyte being quantified.
This method has the advantage of having a detection limit which is lower than that of conventional agglutination methods carried out in the absence of a magnetic field.